Download APEJ-2014-08-0446

Asian Power Electronics Journal, Vol. 9, No. 1, Aug. 2015
Design of Embedded Controller for Various Multilevel
Inverter Topologies
C.R.Balamurugan 1
S.P.Natarajan 2
Abstract– Multilevel inverter technology is an emerging trend
for the control of electric drives in hybrid electric vehicles of
high power rating. This paper proposes three different types
of multilevel inverter topologies they are five level flying
capacitor multilevel inverter, six switch hybrid multilevel
inverter and five switch hybrid multilevel inverter. This
paper analyses the total harmonic distortion of the chosen
three types of multilevel inverter topologies. Embedded
switching pattern scheme is used to improve the performance
of Multilevel Inverter. For this type of inverters pulses are
developed by using the embedded controller. This scheme
reduces the switching loss. The proposed inverter can
synthesize high quality output voltage near to sinusoidal
waves. To validate the developed technique simulations are
carried out through MATLAB/SIMULINK.
Keywords– THD, FCMLI, CMLI, Embedded controller
I. INTRODUCTION
Multilevel inverters (MLI) are plays an important role in
industrial power applications. Generally conventional
MLIs are categorized into diode clamped, flying capacitor
and Cascaded H bridge type. Conventional inverters can
either produce the output levels as zero or maximum. So it
is called a two level inverter. For a high power application,
these types of inverters are not used. Because of it consists
of losses with ripple content, frequency deviations,
switching losses and device ratings. Multilevel Inverters
are tremendously interest to use in Power inverters. The
basic concept of a multilevel inverter is to achieve high
power by using a series of power semiconductor switches
with several lower DC voltage sources to perform the
power conversion by synthesizing a staircase voltage
waveform. Embedded Controllers (ECs) are often found in
low power embedded reference designs, performing a
range of input/output and system management functions.
Embedded controller is a special purpose controller that is
embedded in an electronic system. Embedded controllers
has major role in modern machine and automobile than
power control systems. Embedded controllers are often the
heart of an industrial control system or a process control
application. Krishna Kumar et al [1] proposed a multilevel
inverter topology with input DC sources which are
connected in opposite polarities with one another through
power switches. This approach results in reduced number
of power switches as compared to classical topologies.
K.Gobinath et al [2] developed a novel cascaded
multilevel inverter for harmonic elimination. Jacob James
Nedumgatt et al [3] discussed a new topology of a
cascaded multilevel inverter that utilizes less number of
switches than the conventional topology.
The paper first received 8 Apr. 2014 and in revised form 18 Aug. 2015.
Digital Ref: APEJ-2014-08-0446
1
Department of Electrical Engineering, Arunai Engineering College,
India. E-mail: [email protected]
2
Department of EIE & EEE, Annamalai University, India. E-mail:
[email protected]
R.Bensraj 3
Javad Ebrahimi et al [4] suggested a topology which
reduces the number of DC voltage sources, switches as the
number of output voltage levels increases. Ehsan Najafi et
al [5] presented a new topology with a reversing voltage
component is proposed to improve the multilevel
performance. Roshankumar et al [6] developed a topology
which is obtained by cascading a three-level flying
capacitor inverter with a flying H-bridge power cell in
each phase. K.K. Gupta et al [7] developed a topology for
multilevel inverters which increases the number of levels
as number of switches and conduction losses can be
reduced. Ahmed et al [8] presented two types of
multilevel inverters with reduced number of switches,
losses. G.S. Konstantinou et al [9] proposed a topology
which is a cascaded connection of a conventional three
phase, two level inverter. Arif Al-Judi et al [10] proposed a
Cascaded Multilevel Inverter with reduced number of
Switches. Tehrani et al [11] proposed a new multilevel
inverter topology. Ceglia et al [12] suggested a new
inverter topology using an auxiliary switch which reducing
the number of power devices required to implement a
multilevel output. Leon M et al [13] proposed a multilevel
inverter using carrier based PWM methods. G.Carrara et al
[14] developed a multilevel inverter based on PWM
method. N.S.Choi et al [15] proposed multilevel inverter
that can realize any pulse width modulation scheme which
leads to harmonic reduction.
II. MULTILEVEL INVERTERS
A Multilevel inverter is a power electronic device built
to synthesize a desired A.C voltage from several levels
of DC voltages. Multilevel inverters have gained more
attention in high power applications because it has got
many advantages. It can realize high voltage and high
power output by using semiconductor switches without
the use of transformer and dynamic voltage balance
circuits. The proposed scheme is simulated under the
MATLAB/SIMULINK environment. Filter is not used
at the output side so the THD (Total Harmonic
Distortion) is more. If small size filter is used across the
load the THD will be within the IEEE standard. The
another way to reduce the THD is by increasing the
number of levels of the inverter. The Powergui block
allows you to choose one of the following methods to
solve your circuit (i) Continuous, which uses a variable
step solver from Simulink (ii) Ideal Switching
continuous (iii) Discretization of the electrical system
for a solution at fixed time steps and (iv)Phasor solution.
The Powergui block is necessary for simulation of any
Simulink model containing Sim Power Systems blocks.
It is used to store the equivalent SIMULINK circuit that
represents the state-space equations of the model. When
using this block in a model, you must follow these rules:
Place the Powergui block at the top level of diagram for
optimal performance. You can place it anywhere inside
subsystems for your convenience; its functionality will
not be affected. You can have a maximum of one
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C.R.Balamurugan et. al: Design of Embedded Controller for…
Powergui block per model. You must name the block
powergui. The Powergui block also gives you access to
various Graphical User Interface (GUI) tools and
functions for the steady-state analysis of Sim Power
Systems models, the analysis of simulation results, and
for the design of advanced block parameters. In this
continuous block is chosen in the powergui block.
storage capacitors can provide capabilities during power
outages and also these inverters can provide switch
combination redundancy for balancing different voltage
levels. The input voltage value of this proposed system is
Vdc=200 V and the load R=100ohms.
Fig. 1: Environment block for simpowersystems models
(Powergui)
Fig.3: Half bridge five level flying capacitor inverter for R-phase
Fig. 2: Options available in the Powergui tool
A. Five Level Flying Capacitor Multilevel Inverter
The structure of this flying capacitor inverter is similar to
that of the diode clamped inverter except that instead of
using clamping diodes, the inverter uses capacitors in their
place. The flying capacitor involves series connection of
capacitor clamped switching cells. The Flying Capacitor
(FC)MLI topology has a ladder structure of DC side
capacitors, where the voltage on each capacitor differs
from that of the next capacitor. The voltage increment
between two adjacent capacitor legs gives the size of the
voltage steps in the output waveform. The main advantage
of flying capacitor multilevel inverter is large amounts of
29
Fig.3 shows the general structure of half bridge five level
flying capacitor inverter for R-phase. FCMLI requires 8
semiconductor switches (S1-S4, S1’-S4’) 3 flying
capacitors (C3’, C4’, C5’) and 2 DC link capacitors (C1’,
C2’). This FCMLI consists of four switch pairs (S1,S1’),
(S2,S2’), (S3,S3’) and (S4,S4’). The switches are clamped
by DC-link together with flying capacitors. The four
switches (S1-S4) must be connected in series between DC
input and load and likewise for switches (S4’-S1’). The
three flying capacitors C3’, C4’ and C5’ are charged to
different voltage levels. By changing the transistor
switching states, the capacitors and the DC source are
connected in different ways to produce different load
voltage levels. A typical switch combination used to
synthesize the various load voltages are shown in Table 1.
This proposed five level flying capacitor multilevel
inverter consists of eight switching devices. The switching
states of the multilevel inverter are given as the input for
the embedded controller based proposed system. This
proposed system provides the five output level +2Vdc,
+Vdc, 0, -Vdc, -2Vdc. At the level of 2Vdc, the first four
switches should be turn ON and the remaining switches
will be turned OFF. In the +Vdc level P1, P2, P3, P5
switches will be turned ON. At the level of 0Vdc P1, P2,
P5, P6 should be turned ON. The –Vdc level contains P1,
P5, P6, P7 will be turned ON. At the level of -2Vdc the
lower four switches should be turned ON. This proposed
system used to obtain the five level output, which are
nearer to the sinusoidal output. This proposed system is
used to reduce the THD and it can be used to increase the
performance of the system. It also can be used to reduce
Asian Power Electronics Journal, Vol. 9, No. 1, Aug. 2015
the switching losses. The schematic diagram of proposed
method is shown in the Fig. 3.
Table 1 : Switching states of five-level flying capacitor
multilevel inverter
S1
S2
S3
S4
C3’
C4’
C5’
Vab
1
1
1
1
NC
NC
NC
+Vdc/2
1
1
1
0
NC
NC
+
1
1
0
1
NC
+
-
1
0
1
1
+
-
NC
0
1
1
1
-
NC
NC
0
0
1
1
NC
-
NC
0
1
0
1
-
+
-
0
1
1
0
-
NC
+
1
0
0
1
+
NC
-
1
0
1
0
+
-
+
1
1
0
0
NC
+
NC
1
0
0
0
+
NC
NC
0
1
0
0
-
+
NC
0
0
1
0
NC
-
+
0
0
0
1
NC
NC
-
0
0
0
0
NC
NC
NC
The above table 1 represents the switching states which
are given as the input for the proposed five level flying
capacitor multilevel inverter. By using the embedded
controller the five level output can be obtained for this
proposed system. The simulation output of the proposed
system is shown in Figure 5. The THD which is a measure
of closeness in shape between a waveform and its
fundamental component. When the voltage levels of the
topologies are increases, the harmonic content of the
output voltage waveform decreases significantly.
+Vdc/4
THD 
1
V1

V
n  2 , 3..
2
n
(1)
0
-Vdc/4
-Vdc/2
Fig. 5: Five level output voltage of FCMLI
The THD value for the proposed system is shown in
Figure 6.
Fig. 6: FFT plot for five level output voltage
By seeing the truth table the coding are generated. This
method of generation of pulses is similar to (Selective
Harmonic Elimination) SHE PWM method. The coding
are developed with the help of MATLAB software.
Fig. 4: Sample simulation circuit of five level flying capacitor
multilevel inverter using R load
function y = fcn(u)
a = mod(u*1000,10);
b = mod(u*1000,20);
if a<1.2 %0
p1=1;
p2=1;
p3=0;
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C.R.Balamurugan et. al: Design of Embedded Controller for…
p4=0;
p5=1;
p6=1;
p7=0;
p8=0;
elseif a<3.1 %3
p1=1;
p2=1;
p3=1;
p4=0;
p5=1;
p6=0;
p7=0;
p8=0;
elseif a<7.2 %4
p1=1;
p2=1;
p3=1;
p4=1;
p5=0;
p6=0;
p7=0;
p8=0;
elseif a<9.1 %5
p1=1;
p2=1;
p3=1;
p4=0;
p5=1;
p6=0;
p7=0;
p8=0;
else %0
p1=1;
p2=1;
p3=0;
p4=0;
p5=1;
p6=1;
p7=0;
p8=0;
end
if b<10
y=[p1,p2,p3,p4,p5,p6,p7,p8];
else
y=[p5,p6,p7,p8,p1,p2,p3,p4];
end
B. Six Switch Hybrid Multilevel Inverter
The next proposed circuit is embedded controller based
five level hybrid cascaded inverter with reduced number
of switches is shown in Figure 7. Each separate voltage
source Vdc1, Vdc2, Vdc3 is connected in cascade with other
sources via a special H-bridge circuit associated with it.
The most important part in multilevel inverters is switches
which define the reliability, circuit size, cost, installation
area and control complexity. The first H-bridge circuit
consists of four active switching elements and the second
Voltage Source Inverter (VSI) circuit consists of two
active switching elements that can make the output voltage
either positive or negative polarity or it can also be simply
zero volts which depends on the switching condition of
switches in the circuit.
31
P1
p2
E
a
p3
p4
Embedded
Controller
R
E
L
O
A
D
p5
n
p6
E
Fig. 7: Five level embedded controller based hybrid multilevel
inverter
At the level of 2Vdc, P2, P3, P5 switches should be turned
ON. In the Vdc level P1, P2, P5 will be turned ON and the
remaining switches will turned OFF. The 0Vdc level
contains P2; P3 and P6 switches will be turned ON. At the
level of -Vdc, P1, P2 and P6 switches will be turned ON
and the -2Vdc level contains P1, P4 and P6 switches should
be turned ON. The advantages of cascaded multilevel
inverter are modularized layout and packaging. This
enables the manufacturing process to be done more
quickly and cheaply. In this proposed system the switching
states are given as the input by using the
MATLAB/SIMULINK. The input voltage value of this
proposed system is Vdc=200V and the load R=100ohms.
Table 2 : Switching states for five level proposed hybrid
cascaded multilevel inverter
Switching states
Output
Voltage
P1
P2
P3
P4
P5
P6
0
1
1
0
1
0
2Vdc
1
1
0
0
1
0
Vdc
0
1
1
0
0
1
0
1
1
0
0
0
1
-Vdc
1
0
0
1
0
1
-2Vdc
The switching states of the proposed hybrid multilevel
inverter are shown in Table 2. These switching states are
given as the input and the proposed system produce the
five levels of output. The simulation output of hybrid
multilevel inverter is shown in Figure 8.
Asian Power Electronics Journal, Vol. 9, No. 1, Aug. 2015
Fig. 8: Simulation output of proposed hybrid multilevel
inverter
The total harmonic distortion of the proposed system is
shown in Figure 9.
p4=0;
p5=1;
p6=0;
else %0
p1=0;
p2=1;
p3=1;
p4=0;
p5=0;
p6=1;
end
if b<10
y=[p2,p3,p5,p1,p4,p6];
else
y=[p1,p4,p6,p2,p3,p5];
end
C. Five Switch Hybrid Multilevel Inverter
The next proposed hybrid multilevel inverter is shown in
figure 10. This type of proposed system contains five
switches which produce the five levels of output by using
the embedded controller based MATLAB/SIMULINK.
The input voltage value of this proposed system is
Vdc=200V and the load R=100ohms.
p1
p2
L
O
A
D
E
Fig. 9: THD plot for proposed hybrid multilevel inverter
The coding for six switch hybrid MLI is given below
function y = fcn(u)
a = mod(u*1000,10);
b = mod(u*1000,20);
if a<1.2 %0
p1=0;
p2=1;
p3=1;
p4=0;
p5=0;
p6=1;
elseif a<3.1 %1
p1=1;
p2=1;
p3=0;
p4=0;
p5=1;
p6=0;
elseif a<7.2 %2
p1=0;
p2=1;
p3=1;
p4=0;
p5=1;
p6=0;
elseif a<9.1 %1
p1=1;
p2=1;
p3=0;
p5
Embedded
Controller
E
p3
p4
Fig. 10: Five level Embedded controller based hybrid multilevel
inverter
This proposed system contains five switches which
produce the desired five level output. At the level of +2Vdc,
P1 and P4 switches should be turned ON and the
remaining switches will be turned OFF. In the
+Vdc level P4 and P5 will be turned ON. The 0Vdc level
contains P2 and P4 switches will be turned ON. At the
level of -Vdc, P3 and P5 switches will be turned ON and
the -2Vdc level contains P2 and P3 switches should be
turned ON. The switching states of the above proposed
system are shown in Table 3.
32
C.R.Balamurugan et. al: Design of Embedded Controller for…
Table 3: Switching states for embedded controller based
hybrid multilevel inverter
Switching states
Output
voltage
P1
P2
P3
P4
P5
1
0
0
1
0
2Vdc
0
0
0
1
1
Vdc
0
1
0
1
0
0
0
0
1
0
1
-Vdc
0
1
1
0
0
-2Vdc
By using these switching states the Hybrid MLI can
produce five levels of output. The simulation output of the
proposed system is shown in Figure 11.
Fig. 11: Simulation output of embedded controller based
hybrid multilevel inverter
The total harmonic distortion of the proposed five level
hybrid multilevel inverter is shown in Figure 12.
elseif a<3.1 %1
p1=0;
p2=0;
p3=0;
p4=1;
p5=1;
elseif a<7.2 %2
p1=1;
p2=0;
p3=0;
p4=1;
p5=0;
elseif a<9.1 %1
p1=0;
p2=0;
p3=0;
p4=1;
p5=1;
else %0
p1=0;
p2=1;
p3=0;
p4=1;
p5=0;
end
if b<10
y=[p1,p4,p2,p3,p5];
else
y=[p2,p3,p1,p4,p5];
end
In a Direct Current (DC) circuit, voltage or current is
simple to define, but in an Alternating Current (AC) circuit,
the definition is more complicated, and can be done in
several ways. Root Mean Square (RMS) refers to the most
common mathematical method of defining the effective
voltage or current of an AC wave. The number of pulses p
per half cycle depends on the carrier frequency. By
varying the modulation index ma, the RMS output voltage
can be varied. The area of each pulse corresponds
approximately to the area under the sine wave between the
adjacent midpoints of off periods on the gating signals. If
δm is the width of the mth pulse, the RMS output voltage
can be expressed as follows:
VRMS  Vdc
Fig. 12: THD plot for Embedded Controller based hybrid
multilevel inverter
The program for the five switch MLI is given below
function y = fcn(u)
a = mod(u*1000,10);
b = mod(u*1000,20);
if a<1.2 %0
p1=0;
p2=1;
p3=0;
p4=1;
p5=0;
33
2p
m

(2)
m 1
Table 4 shows the output obtained for the three topologies
chosen. Comparing the different topology of 5-level
inverter it is observed that 5-level hybrid five switch MLI
requires lesser number of switches. But comparing the
performance of the different topology almost three of the
MLI provides similar performance only. In the case of five
levels hybrid six switches MLI is the combination of Hbridge and VSI inverter. The H-bridge and Voltage source
inverter produce 3-levels. These two circuits are connected
in series so total output is five levels. In five levels hybrid
five switches MLI is the combination of H-bridge and
Diode bridge rectifier with one switch. Both circuits
produce three levels. By adding five level is obtains as a
final output. To implement the inverter it is possible select
the Field Programmable Gate Array (FPGA)/dSPACE to
generate gate pulse for the switches used. Power circuits
are developed with Power (Metal Oxide Semiconductor
Asian Power Electronics Journal, Vol. 9, No. 1, Aug. 2015
Field Effect Transistor) MOSFET and Power diodes. The
voltage sources used for hardware may be from battery or
through solar panels. Control circuit consists of MOSFET
driver circuit, opto coupler and FPGA/dSPACE controller.
Table 4: Parameters of three proposed topologies
Number
of
switches
Topology
THD
Vrms
5-Level FCMLI
8
20.47%
197
5-Level Hybrid
six switch MLI
6
20.47%
197
5-Level Hybrid
five switch MLI
5
20.77%
196.3
Table 5: Comparison of power component requirement for
the chosen inverters
5-Level
FCMLI
Topology
5-Level
Hybrid
6-switch
MLI
6
5-Level
Hybrid
5-switch
MLI
5
Main
Switching
devices
Main diodes
8
8
6
10
Clamping
capacitors
12
-
-
DC bus
Capacitors
4
-
-
DC voltage
sources
1
3
2
III. CONCLUSION
In these paper three types of embedded controller based
multilevel inverter topologies are proposed. The
topologies are five level flying capacitor multilevel
inverter, six switch five level hybrid multilevel inverter
and five switch hybrid MLI topologies. The most
important feature of the hybrid multilevel inverter is being
convenient for expanding and increasing the number of
output levels simply with less number of switches. The
switching losses also reduced and the performance of the
system will be increased. The total harmonic distortion
value of the embedded controller based proposed
topologies are reduced than the conventional topologies.
The total harmonic distortion value of proposed topologies
is 20.47%, 20.47% and 20.77%.
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BIOGRAPHIES
Dr. C.R.Balamurugan was born in 1978 in
Kumbakonam. He has obtained B.E
(Electrical and Electronics), M.E (Power
Electronics and Drives) degree and Ph.D
(MultiLevel Inverters) in 2000, 2005 and
2015 respectively from Arunai Engineering
College,
Tiruvannamalai,
Sathyabama
University, Chennai and Annamalai
University, Chidambaram. He has been
working in the teaching field for about 12
years. His areas of interest include power
electronics, electrical machines and solar energy systems. He has 60
publications in international journals. His research papers 50 have been
presented in various/IEEE international/national conferences. Currently,
he is working as Associate Professor in the Department of EEE, Arunai
Engineering College, Tiruvannamalai. He is a life member of Instrument
Society of India and Indian Society for Technical Education. Contact
number- +91-9894522351. E-mail:[email protected].
Dr. S.P.Natarajan was born in 1955 in Chidambaram. He has obtained
B.E (Electrical and Electronics) and M.E (Power Systems) degrees in
34
C.R.Balamurugan et. al: Design of Embedded Controller for…
1978 and 1984 respectively from Annamalai
University securing distinction and then Ph.D
in Power Electronics from Anna University,
Chennai in 2003. He is Former Professor and
Head
of
Instrumentation
Engineering
Department at Annamalai University where he
has put in 31 years of service. He produced
eight Ph.Ds and presently guiding eight Ph.D
Scholars and so far guided eighty M.E students.
His research papers 66 have been presented in
various/IEEE international/national conferences in Mexico, Virginia,
Hong Kong, Malaysia, India, Singapore and Korea. He has 20
publications in national journals and 100 in international journals. His
research interests are in modeling and control of DC-DC converters and
multiple connected power electronic converters, control of permanent
magnet brushless DC motor, embedded control for multilevel inverters
and matrix converters etc. He is a life member of Instrument Society of
India and Indian Society for Technical Education. Contact number- +919443185211. Email: [email protected].
Dr.R.Bensraj was born in 1973 in
Marthandam. He has obtained B.E
(Electrical and Electronics), M.E (Power
Systems) and Ph.d (Multilevel Inverter)
degrees from Annamalai University,
Chidambaram. He has been working in the
teaching field for about 13 years. His areas
of interest include power electronics,
electrical machines and solar energy
systems. He has 32 publications in
international journals. His research papers
10 have been presented in various/IEEE international/national conferences.
Currently, he is working as Associate Professor in the Department of EEE,
Annamalai University, Chidambaram. He is a life member of Indian Society
for Technical Education. Contact number- +91-9443929992. Email:[email protected].
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